Lithium salts, in particular Lithium Carbonate, are widely utilized for the prophylaxis and the treatment of mania, maniacal depression, bipolar mania and unipolar mania. The conventional formulations of Lithium salts cause a rapid gastroenteric absorption, which determines the necessity of repeated dosings during the day.
Furthermore, in planning formulations containing Lithium, it has to be borne in mind that the margin between the therapeutic concentration and the toxic concentration is very small and the side effects reported during the therapy are often due to the overcoming of the toxic dose, in particular in sensitive patients and in elderly people.
Several techniques are described allowing the obtainment of Lithium salt formulations for the above stated psychiatric treatments. For example, patent EP 0222 411 B1 allows to obtain a multiparticulate formulation suitable for Lithium salt administration, but it has to use saccharose crystals for the formation of particles containing Lithium salt, with the consequence that the obtainable dosages are low.
Moreover, for the particle coating, fats with low melting points have to be used, which limits the dissolution characteristics.
U.S. Pat. No. 5,445,829 allows to prepare prolonged release multiparticulates, but requires, anyway, the use of a core or inert substratum to carry the drug and, therefore, the obtainable formulations are not suitable for high dosages of the active ingredient.
To obtain suitable dosages for the Lithium therapy, i.e. 0.4-1.2 g/day in the prophylaxis and up to 2 g/day in the acute treatment of states of mania, the use of tablet formulations is frequent. We cite, for example, the formulation referred to in U.S. Pat. No. 4,264,573, in which the Lithium Carbonate content is high (70-80%), but the disadvantage is represented by the monolithic form. The patent EP 471 100 describes controlled release tablets obtained through the matrix technique, having 400 mg of Lithium Carbonate per tablet. Said tablets have the disadvantage of a too low dosage for the most of the therapeutic purposes; additionally, they exhibit the same disadvantages of the monolithic forms.